1. Field of the Invention
The present invention relates to a high-magnification zoom lens system, and more specifically, to a high-magnification zoom lens system for use in a lens shutter camera.
2. Description of the Prior Art
Optical systems for use in lens shutter cameras are required to be compact and of high magnification. In recent years, high magnification is particularly required for such optical systems.
In order to realize a compacter lens system, in Japanese Laid-open Patent Application No. H3-127012, an arrangement is proposed having four lens elements grouped into two units with a zoom ratio of approximately 2 to 2.5.times.. In order to realize a higher magnification, three-unit zoom lens systems of positive, positive, negative configuration have been used since they are advantageous in performance correction and the amount of lens movement is small.
However, if a zoom ratio of 2.5 to 3.times. or higher is achieved in the two-unit, four-lens-element arrangement of Japanese Laid-open Patent Application No. H3-127012, it is difficult to secure a required performance, and the amount of lens movement is large. Consequently, it is impossible to realize a compact, high-magnification optical system.
In the above-mentioned three-unit zoom lens systems of positive, positive, negative configuration, because of the arrangement thereof, plus distortion is apt to be generated at a shorter focal length condition. Restraining this is one of the problems in designing such lens systems. Moreover, in positive first lens units of the three-unit lens systems of positive, positive, negative configuration, it is typical that the most object side lens element is convex to the object side. For this reason, more number of lens elements are required in order to correct the plus distortion generated at a shorter focal length condition.